We have developed a new probe for fluorescence in situ hybridization (FISH) which identifies less than 5 Mb of DNA from the terminal q-arm of human chromosome 9. More than 2/3 of the portion of chromosome 9 identified by this probe remains with the 9 in the translocation associated with CML while less than 1/3 becomes part of the Ph chromosome. Experiments on bone marrow samples from normal healthy volunteers and CML patients reveal this probe to be highly effective in detecting the translocation in interphase cells -- two intense domains of fluorescence in normal cells while two intense plus a third less intense domain are present in CML cells. The large size of the probe also enables the detection of the translocation in metaphase cells with high efficiency. Here, we will further increase the efficiency of the probe by essentially eliminating false positives by combining it with a BCR cosmid contig in 2- color FISH, and by reducing the already low percentage of unscorable cells in the cultured preparations. Most importantly we will use the ability of the probe to measure the frequencies of Ph+ cells in quiescent interphase populations as well as cycling metaphase cells in CML patients at diagnosis and at various time points after treatment in order to determine which parameter is most effective in predicting outcome. Patient cadres from all the different treatment regimens associated with this Program will be so evaluated. Data will also be compared and evaluated with the Program Project that will be determining the presence of cells expressing fusion protein in these same patient sets. The FISH probe will also be used to relate the frequency of Ph+ cells before and after autologous bone marrow transplantation to successful outcome. The most efficacious FISH probe system for evaluating the frequency of Ph+ cells will be made available to projects involved in separations of normal from cancer cells or cells of different lineages or proliferative states, and to the Cytogenetics Core for their use in problems associated with this Program.